CA1061454A - Gain control device of video signal reproducing apparatus - Google Patents
Gain control device of video signal reproducing apparatusInfo
- Publication number
- CA1061454A CA1061454A CA201,905A CA201905A CA1061454A CA 1061454 A CA1061454 A CA 1061454A CA 201905 A CA201905 A CA 201905A CA 1061454 A CA1061454 A CA 1061454A
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- CA
- Canada
- Prior art keywords
- circuit
- signal
- circuits
- gain control
- variable gain
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/79—Processing of colour television signals in connection with recording
- H04N9/793—Processing of colour television signals in connection with recording for controlling the level of the chrominance signal, e.g. by means of automatic chroma control circuits
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/76—Television signal recording
- H04N5/91—Television signal processing therefor
- H04N5/93—Regeneration of the television signal or of selected parts thereof
- H04N5/931—Regeneration of the television signal or of selected parts thereof for restoring the level of the reproduced signal
Abstract
ABSTRACT OF THE DISCLOSURE
A gain control circuit for a video signal reproducing apparatus provides a variable gain circuit in the repro-duced video signal path and an amplitude detector cir-cuit to which a pilot signal separated from the repro-duced video signals is applied. The gain control circuit has N series circuits, each consisting of a series-connected capacitor and a switching element, each of the series circuits corresponding to one of the trans-ducers of the video signal reproducing apparatus. The series circuits are connected to form a parallel circuit across which is applied an output signal from the am-plitude detector circuit to supply a gain control signal to the variable gain circuit. Further, each switching element of the series circuits is controlled to be conductive only during the intervals during which a reproduced video signal is obtained from a corresponding rotary head.
A gain control circuit for a video signal reproducing apparatus provides a variable gain circuit in the repro-duced video signal path and an amplitude detector cir-cuit to which a pilot signal separated from the repro-duced video signals is applied. The gain control circuit has N series circuits, each consisting of a series-connected capacitor and a switching element, each of the series circuits corresponding to one of the trans-ducers of the video signal reproducing apparatus. The series circuits are connected to form a parallel circuit across which is applied an output signal from the am-plitude detector circuit to supply a gain control signal to the variable gain circuit. Further, each switching element of the series circuits is controlled to be conductive only during the intervals during which a reproduced video signal is obtained from a corresponding rotary head.
Description
BACKGROUND OF THE INVENTION
_eld of the Invention This invention relates to a gain control device of a ~ideo signal reproducing apparatus and particularly to a gain control device suitable for use in an automatic color control circuit of a color ~ideo signal repro-ducing apparatus, BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 are waveform diagrams used for explaining the invention;
Figure 3 is a systematic diagram showing one embodiment of the invention;
Figure 4 is a wave~orm diagram used îor explaining the embo-diment of the invention shown in Figure 3; and Figure 5 is a systematic diagram showing another embodiment.
of the invention.
_eld of the Invention This invention relates to a gain control device of a ~ideo signal reproducing apparatus and particularly to a gain control device suitable for use in an automatic color control circuit of a color ~ideo signal repro-ducing apparatus, BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 are waveform diagrams used for explaining the invention;
Figure 3 is a systematic diagram showing one embodiment of the invention;
Figure 4 is a wave~orm diagram used îor explaining the embo-diment of the invention shown in Figure 3; and Figure 5 is a systematic diagram showing another embodiment.
of the invention.
-2- ~:~
10~1454 Descri tion of the Prior Art P
There has hitherto been proposed a color video tape recorder having~ for example~ two rotary magnetic heads in which a color video signal at every field is recorded by these heads so that one magnetic track of each field is alternately formed on a magnetic tape obliquely to its longi-tudinal direction~ while a color video signal at every field is reproduced by these heads alternately from the magnetic track of each field, In the color video tape recorder of this kind, a chrominance signal in the repro-duced signal is sometimes varied in level according to these heads due to irregular characteristics of these heads~ unequal characteristics of ampli-fying systems~ uneven contact to the tape or the like. When a color video signal having such a chrominance signal with variable level is applied to a television receiver for producing a picture~ the color flicker is undesirably yielded in the reproduced picture.
In the case when the contact of heads to a tape is irregular~
the waveforms of chrominance signals EA and EB reproduced from two ;
rotary heads become as shown in Figure 1A~ in which the level fluctuation appears at every field in the respective signals EA and EB.
Meantime~ in the case when the characteristics of two rotary heads or ~hose of the respective amplifyings ystems are not uniform, the wa-~ m~i of the respective chrominance signals EA and EB reprodllced from ~hesç rotary heads are such as shown in Figure 1B~ wherein the res-pective signals EA and EB are different in level from each other but each level is constar t in each field.
Generally~ these causes are very often complicated. In this caseJ the waveform~th)e chrominance signals EA and EB reproduced from two rotary heads become as shown in Figure 1C, wherein the waveforms of Figures 1A and 1B are mixed up, It has already been known that a variable gain circuit is provided in the transmitting path of chrominance signals and the gain of the .~
106~S4 above eircuit is eontrolled aeeording to the level of a burst signal separated from the ehrominanee signals~ thus the levels of the reproduced chrominance signals being made eonstant.
However~ in ordèr to eliminate the level variation of the ehro-minanee signals as shown in Figure 1 C, the response speed of gain variation in the variable gain eireuit must be selected to be quite high~ but its per-formanee is diffieult.
- AeeordinglyJ there has been proposed an idea to provide a eonstant level of chrominanee signals in sueh a manner that a burst signal is applied to an amplitude deteetor eireuit sueh as a synchronous detector eireuit to derive therefrom a deteeted output whieh is applied to a hold cireuitand the output of this hold eireuit is then applied to the variable gain eircuitas a variable gain eontrol signal. In this ease~ the level variation of the ehrominanee signal in eaeh field aeeording to each rotary head as shown in Figure 1A is once removed~ but the following drawback is accompanied.
In other words, the level of the chrominanee signal in eaeh field is eonstant as shown in Figure 1 B~ However, in the case when the level is different for every rotary head~ the output signals FA and FB of the hold circuit eorresponding to eaeh rotary head provide slanting rise and deeay portions therebetween as shown in Figure 2A. As a result, the reprodueed ehromi-nance signals as shown in Figure 1 B are varied by the variable gain circuit in such a ~anner that the intermediate level at every field is made constant, but the joint portion of the fields~ that is, the changed-over portion of the ehrominance signal reproduced from eaeh rotary head jumps up as shown in Figure 2B, This is eaused by the faet that since a burst signal is provided at every horizontal period, the response to variable gain can not be hastened and practically is further delayed due to noise or the like, SUMMARY OF THE INVENTION
-Accordingly~ a main object of this invention is to provide a - 30 ~ gain eontrol device of a video signal reprodueing apparatus in whieh the level ~ariation of video signals reproduced from its rotary heads can be positive-ly removed.
Another object of this invention is to provide a gain control device of a ~ideo signal reproducing apparatus in which pulse rise and decay times of an output signal corresponding to each rotary rnagnetic head are substantially ~ero, A further object of this invention is to provide a gain contrsl device of a video signal reproducing apparatus in which even though a reproduced chrorrlinance signal is rapidly changed in level, the same il!;
corrected to be constant in level so that color shading may not occur in the reproduced picture.
A still îurther object of this invention is to provide a gain control device of a video signal reproducing apparatus in which not only a chrominance signal from each rotary magnetic head is made constant in level but also a lurr~inance signal therefrom is made constant in level.
A further another object of this invention is to provide a gain control device of a video signal reproducing apparatus in which the occurrence of color flicker in a reproduced picture is positively elirninated to obtain a color reproduced picture of good quality.
A still further another object of this invention is to provide a gain control device of a video signal reproducing apparatus such that particularly complicated operation is not required and its construction is simple .
. In accordance with the foregoing objects, there is provided:-a gain control circuit for a video signal reproducing apparatus comprising a plurality of trans-ducers to reproduce recorded video signals, said circuit comprising:
A. a plurality of variable gain circuits each connected to a respective one of said transducers to receive reproduced video signals therefrom;
~ -5-~6~454 B. means to separate a predetermined signal from the reproduced video signals;
C. an amplitude detector circuit connected to the signal separating means; and D. a plurality of series circuits corresponding in number to the number of said transducers and each comprising a capacitor and a switching element connected in series, all of the series circuits being connected in parallel to a common junction to form a parallel circuit, said common junction being connected to the output of the amplitude detector circuit to have the output voltage of the detector circuit impressed across the parallel circuit, said common junction being further connected to all of the variable gain circuits to simultaneously supply said detector circuit output to all of said variable gain circuits to control the gains thereof, and means for selectively energizing each switching element in each of the series circuits to cause each of the series circuits to be conductive only when a reproduced video signal from the respective transducer corresponding to the series circuit is applied to the respective variable gain circuit so that the voltage at said common junction is substantially . The other objects~ features and advantages of the present invention will be apparent from the following description taken in conjunc-tion with the accompanying drawings~
DESCRIPTION OF THE PREFERRED EMBOD1~1ENT
A description will hereinafter be given on one embodiment of this invention with reference to Figures 3 and 4.
~ -5a-~ . "
106~454 In Figure 3~ rotary magnetic heads 1A and 1B are disposed with an angular distance of 180 therebetween to reproduce color video signals îrom a magnetic tape alternately at e~ery îield. These reproduced - -5b-~061454 outputs are supplled respectively through reproduction ampli-fiers 2A and 2B and further through buffer amplifiers 3A and 3B to a switching circuit 4. The changed-over output therefrom is applied to a high-pass filter 5 to derive therefrom a frequency-modulated luminance signal which is applied through a llmiter circuit 6 to a frequency demodulator 7 for being demodulated. The demodulated output therefrom is then applied through a low-pass filer 8 and a delay line ~ to an adder lO.
The changed-over output is also applied to a low-pass filter 12 lQ to derive therefrom a chrominance signal which is frequency-converted to a lower frequency side, that is, arranged to have the carrier frequency of lower than 3.58MHz, for example, 767KHz. The chrominance signal thus obtained is further applied through a variable gain circuit 13 to a frequency converter circuit 14. Meanwhile, a signal having a frequency of 3.58MHz from a fixed frequency oscillator 16 and a signal having a fre-quency fc from a variable frequency oscillator 18 are applied to a frequency converter circuit 1~ to derive therefrom a signal having a frequency of (3.58MHz + fc); This signal is 2Q applied through a band-pass filter 20 to the frequency converter circuit 14 thereby obtaining a chrominance signal which is converted to the original frequency, that is, arranged to have a color subcarrier frequency of 3.58MHz. Then, this chrominance signal is applied through a band-pass filter 15 to the adder 10.
The output from the band-pass filter 15 is partially supplied to the base of the transistor 35a forming a burst gate circuit 35. Meanwhile, the output from the low-pass filter 8 is also applied to a horizontal synchronizing signal separation circuit 21 to separate therefrom a horizontal synchronizing 3Q signal. This horizontal synchronizing signal is applied to a signal forming circuit 22 to form a burst signal pickup signal which is applied to the base of the transistor 35a, too.
~06~454 A ~urst signal from the ~urst gate circuit 35 is appl~ed to a phase comparison circuit 17 for ~eing compared ~ith the phase of the signal having the reference frequency of
10~1454 Descri tion of the Prior Art P
There has hitherto been proposed a color video tape recorder having~ for example~ two rotary magnetic heads in which a color video signal at every field is recorded by these heads so that one magnetic track of each field is alternately formed on a magnetic tape obliquely to its longi-tudinal direction~ while a color video signal at every field is reproduced by these heads alternately from the magnetic track of each field, In the color video tape recorder of this kind, a chrominance signal in the repro-duced signal is sometimes varied in level according to these heads due to irregular characteristics of these heads~ unequal characteristics of ampli-fying systems~ uneven contact to the tape or the like. When a color video signal having such a chrominance signal with variable level is applied to a television receiver for producing a picture~ the color flicker is undesirably yielded in the reproduced picture.
In the case when the contact of heads to a tape is irregular~
the waveforms of chrominance signals EA and EB reproduced from two ;
rotary heads become as shown in Figure 1A~ in which the level fluctuation appears at every field in the respective signals EA and EB.
Meantime~ in the case when the characteristics of two rotary heads or ~hose of the respective amplifyings ystems are not uniform, the wa-~ m~i of the respective chrominance signals EA and EB reprodllced from ~hesç rotary heads are such as shown in Figure 1B~ wherein the res-pective signals EA and EB are different in level from each other but each level is constar t in each field.
Generally~ these causes are very often complicated. In this caseJ the waveform~th)e chrominance signals EA and EB reproduced from two rotary heads become as shown in Figure 1C, wherein the waveforms of Figures 1A and 1B are mixed up, It has already been known that a variable gain circuit is provided in the transmitting path of chrominance signals and the gain of the .~
106~S4 above eircuit is eontrolled aeeording to the level of a burst signal separated from the ehrominanee signals~ thus the levels of the reproduced chrominance signals being made eonstant.
However~ in ordèr to eliminate the level variation of the ehro-minanee signals as shown in Figure 1 C, the response speed of gain variation in the variable gain eireuit must be selected to be quite high~ but its per-formanee is diffieult.
- AeeordinglyJ there has been proposed an idea to provide a eonstant level of chrominanee signals in sueh a manner that a burst signal is applied to an amplitude deteetor eireuit sueh as a synchronous detector eireuit to derive therefrom a deteeted output whieh is applied to a hold cireuitand the output of this hold eireuit is then applied to the variable gain eircuitas a variable gain eontrol signal. In this ease~ the level variation of the ehrominanee signal in eaeh field aeeording to each rotary head as shown in Figure 1A is once removed~ but the following drawback is accompanied.
In other words, the level of the chrominanee signal in eaeh field is eonstant as shown in Figure 1 B~ However, in the case when the level is different for every rotary head~ the output signals FA and FB of the hold circuit eorresponding to eaeh rotary head provide slanting rise and deeay portions therebetween as shown in Figure 2A. As a result, the reprodueed ehromi-nance signals as shown in Figure 1 B are varied by the variable gain circuit in such a ~anner that the intermediate level at every field is made constant, but the joint portion of the fields~ that is, the changed-over portion of the ehrominance signal reproduced from eaeh rotary head jumps up as shown in Figure 2B, This is eaused by the faet that since a burst signal is provided at every horizontal period, the response to variable gain can not be hastened and practically is further delayed due to noise or the like, SUMMARY OF THE INVENTION
-Accordingly~ a main object of this invention is to provide a - 30 ~ gain eontrol device of a video signal reprodueing apparatus in whieh the level ~ariation of video signals reproduced from its rotary heads can be positive-ly removed.
Another object of this invention is to provide a gain control device of a ~ideo signal reproducing apparatus in which pulse rise and decay times of an output signal corresponding to each rotary rnagnetic head are substantially ~ero, A further object of this invention is to provide a gain contrsl device of a video signal reproducing apparatus in which even though a reproduced chrorrlinance signal is rapidly changed in level, the same il!;
corrected to be constant in level so that color shading may not occur in the reproduced picture.
A still îurther object of this invention is to provide a gain control device of a video signal reproducing apparatus in which not only a chrominance signal from each rotary magnetic head is made constant in level but also a lurr~inance signal therefrom is made constant in level.
A further another object of this invention is to provide a gain control device of a video signal reproducing apparatus in which the occurrence of color flicker in a reproduced picture is positively elirninated to obtain a color reproduced picture of good quality.
A still further another object of this invention is to provide a gain control device of a video signal reproducing apparatus such that particularly complicated operation is not required and its construction is simple .
. In accordance with the foregoing objects, there is provided:-a gain control circuit for a video signal reproducing apparatus comprising a plurality of trans-ducers to reproduce recorded video signals, said circuit comprising:
A. a plurality of variable gain circuits each connected to a respective one of said transducers to receive reproduced video signals therefrom;
~ -5-~6~454 B. means to separate a predetermined signal from the reproduced video signals;
C. an amplitude detector circuit connected to the signal separating means; and D. a plurality of series circuits corresponding in number to the number of said transducers and each comprising a capacitor and a switching element connected in series, all of the series circuits being connected in parallel to a common junction to form a parallel circuit, said common junction being connected to the output of the amplitude detector circuit to have the output voltage of the detector circuit impressed across the parallel circuit, said common junction being further connected to all of the variable gain circuits to simultaneously supply said detector circuit output to all of said variable gain circuits to control the gains thereof, and means for selectively energizing each switching element in each of the series circuits to cause each of the series circuits to be conductive only when a reproduced video signal from the respective transducer corresponding to the series circuit is applied to the respective variable gain circuit so that the voltage at said common junction is substantially . The other objects~ features and advantages of the present invention will be apparent from the following description taken in conjunc-tion with the accompanying drawings~
DESCRIPTION OF THE PREFERRED EMBOD1~1ENT
A description will hereinafter be given on one embodiment of this invention with reference to Figures 3 and 4.
~ -5a-~ . "
106~454 In Figure 3~ rotary magnetic heads 1A and 1B are disposed with an angular distance of 180 therebetween to reproduce color video signals îrom a magnetic tape alternately at e~ery îield. These reproduced - -5b-~061454 outputs are supplled respectively through reproduction ampli-fiers 2A and 2B and further through buffer amplifiers 3A and 3B to a switching circuit 4. The changed-over output therefrom is applied to a high-pass filter 5 to derive therefrom a frequency-modulated luminance signal which is applied through a llmiter circuit 6 to a frequency demodulator 7 for being demodulated. The demodulated output therefrom is then applied through a low-pass filer 8 and a delay line ~ to an adder lO.
The changed-over output is also applied to a low-pass filter 12 lQ to derive therefrom a chrominance signal which is frequency-converted to a lower frequency side, that is, arranged to have the carrier frequency of lower than 3.58MHz, for example, 767KHz. The chrominance signal thus obtained is further applied through a variable gain circuit 13 to a frequency converter circuit 14. Meanwhile, a signal having a frequency of 3.58MHz from a fixed frequency oscillator 16 and a signal having a fre-quency fc from a variable frequency oscillator 18 are applied to a frequency converter circuit 1~ to derive therefrom a signal having a frequency of (3.58MHz + fc); This signal is 2Q applied through a band-pass filter 20 to the frequency converter circuit 14 thereby obtaining a chrominance signal which is converted to the original frequency, that is, arranged to have a color subcarrier frequency of 3.58MHz. Then, this chrominance signal is applied through a band-pass filter 15 to the adder 10.
The output from the band-pass filter 15 is partially supplied to the base of the transistor 35a forming a burst gate circuit 35. Meanwhile, the output from the low-pass filter 8 is also applied to a horizontal synchronizing signal separation circuit 21 to separate therefrom a horizontal synchronizing 3Q signal. This horizontal synchronizing signal is applied to a signal forming circuit 22 to form a burst signal pickup signal which is applied to the base of the transistor 35a, too.
~06~454 A ~urst signal from the ~urst gate circuit 35 is appl~ed to a phase comparison circuit 17 for ~eing compared ~ith the phase of the signal having the reference frequency of
3.58MHz from the oscillator 16. Thus compared DC output is used to control the oscillation frequency of the oscillator 18 and hence the frequency of the frequency converting signal which is applied from the frequency converter circuit l9 through the ~and-pass filter 20 to the circuit 14, thus a so-called jitter correction ~eing performed.
The variable gain circuit 13 in this e}nbodiment is composed of a two-stage amplifier circuit having transistors 43 and 44 and a variable attenuator consisting of a resistor 41 and a variable impedance field effect transistor 40, both being connected in a reverse-L shape. The variable attenuator is provided at the input side of the first-stage transistor 43.
A series circuit consisting of a capacitor 32A and a field effect transistor 30A served as a switching element and another series circuit consisting of a capacitor 32B and a field effect transistor 30B served as a switching element are connected in parallel with each other, the parallel circuit being connected at one end thereof through a resistor 34 to the gate of the field effect transistor 40 of the circuit 13 and at the other end thereof to the ground.
These field effect transistors 30A and 30B are corresponding to the rotary magnetic heads lA and lB, respect-ively, each being controlled to be turned on only during the period ~here a reproduced video signal is being derived from the corresponding rotary magnetic head lA or lB. To this end, according to the rotation of the rotary magnetic heads lA and 3Q lB two pulse signals having phase different of 180 there-between are adapted to be obtaina~le at every rotation thereof and supplied to input terminals 25 and 26, respectively. These 10614S~
pulse signals are respectively applied to monostable multi-vi~rators 27 and 2 8 to be delayed for a predetermined time so as to correspond to the signal change-over times of the rotary magnetic heads lA and lB. Thereafter, these signals are applied to a flip-flop c~rcuit 29 to produce outputs having polarities different from each other, which are then applied to the bases of the field effect transistors 3QA and 30B, respectively, to turn-on the both alternately. In this case, one of these outputs from the flip-flop circuit 29is supplied to the switching circuit 4 as a switching control signal.
The ~urst signal from the burst gate circuit 35is also applied to a limiter circuit 36 serving as a wave shaping circuit to produce a rectangular-wave signal having constant amplitude which is applied as a control signal or a gate signal to a synchronous dete.ctor circuit 37 serving as an amplitude detector circuit.
The detector circuit 37 comprises a transistor 46 to which a signal from tne limiter circuit 36is applied for being amplified, a transformer 47 whose primary winding 47Ais 2Q connected to the collector of the transistor 46 and whose secondary winding 47Bis connected thereacross with a series connection consisting of a capacitor 49A, a diode 50A, a resis-tor 51A, a resistor 51B, a diode 50B and a capacitor 49B, and a series circuit consisting of resistors 52A and 52B which is connected between the connection mid-point of the diode 49A and the diode 50A and the connection mid-point of the diode 50B and the capacitor 49B. The connection mid-point of the resistors 51A and 51Bis applied with a E1ias from a variable resistor 55 and the burst signal from the burst gate circuit 35. Further, the mid-point of the secondary winding 47B of the transformer 47 is connected to the connection mid-point between the resistors 52A and 52B.
The output of the detector circu~t 37 is derived from the connection }nid-point of the resistors 52A and ~2B, that is, its output terminal and applied across both ends of the parallel circuit consisting of the series circuit of capacitor 32A and field effect transistor 30A and the series circuit of capacitor 32~3 and field effect transistor 30B. Reference character + B
represents a power source.
A description will next be given on the operation and effect of the apparatus shown in Figure 3. The field effect transistors 30A and 3QB each serving as a switching element are turned on respectively only during the period where the reproduced video signal is being derived from the corresponding rotary magnetic head lA or lB. On the other hand, the opposite ends of the secondary winding 47B of the transformer 47 are alternately inverted in polarity based on the outputs of the primary winding 4 7A . When the end portion of the secondary winding 47B at the side of capacitor 49B becomes positive in polarity, a signal flows through a loop of primary winding 47B-capacitor 49B - diode 50B - resistor 51B - resistor 51A - diode 2Q 50A - capacitor 49A - secondary winding 47B, so that the diodes 50A and 50B are turned on only during the period of half cycle of the signal at every half cycle thereof. Therefore, if the transformer 47 is previously adjusted, the half cycle period during which diodes 50A and 50s are being turned on can be conformed with, for example, a positive half cycle period of the burst signal. Accordingly, in this case, a portion of this burst signal at a positive half cycle flows through two paths of burst gate circuit 35 - resistors 51A, 51B - diodes 50A, 50B -capacitors 49A, 49B - middle point of secondary winding 47B to the capacitor 32A or 32B to charge the same up to the peak value of the burst signal. The voltage across the capacitor 32A or 32B is then applied through the resistor 34 to the gate of the _g _ 1061~54 field effect transistor 40 of t~e variable gain circuit 13. In this case, when the ~ield effect. transistors 3QA and 3QB are respectively in off-state, the voltages across the corresponding capacitors 32A and 32B are held at the values immediately before they are turned off. As a result, a variable control signal applied to the field effect transistor 40 becomes as shown in Figure 4 suc~ that slopes disappear at the pulse rising and falling portions between the output signals FA and FB corres-ponding to t~s respective rotary magnetic heads, that is, the pulse rising and falling times thereof become nearly zero.
Accordingly, the chrominance signal derived from the variable gain circuit 13 Cthat is, the chrominance signal converted into low frequency~ will have a constant level independent of the difference of the rotary magnetic heads lA and lB. In other words, even if video signals reproduced from the rotary magnetic heads lA and lB, that is, the chrominance signals in this case are of level variation type such as shown in Figure 1, the variable gain circuit 13 can yield chrominance signals such as having constant level and causing no jumping-up at a time point when the signals from the respective rotary magnetic heads lA
and lB are changed-over.
Furthermore, according to the present apparatus, the diodes 50A and 50B are turned on based on the signal having constant amplitude derived from the limiter circuit 36 and a portion of the ~urst signal at, for example, a positive half cycle is picked out according to these conductive diodes 50A
and 50B. merefore, a variable gain control signal of quick rising can be obtained without any time lag due to the threshold level of the diodes 50A and 50B being caused and also without any influence of d layed operation of the diodes 50A and 50B themselves being effected. As a re-sult, even if a reproduced chrominance signal is rapidly changed in level, the signal can be corrected to be constant in level with the result that there is no possibilitv of producing color shading on the reproduced picture.
lQ614S4 In addition, the phase con~ormab-lity ~etween the signal derived from t~ limiter circuit 36 and the ~urst signal can be ac~ieved only by adjusting the transformer 47 particu-larly with nocomplicated operation being required and with a simple construction, too.
The variable gain circuit 13 in Figure 3 may be provided at the output side of the band-pass filter 15. In this case, a chrominance signal having carrier frequency reconverted to the original value 3.58MHz will be made constant in level.
The apparatus in Figure 3 is described of the case ~here the variable gain circuit is provided in transmitting path of chrominance signals. However, it is also possible to provide variable gain circuits in transmitting paths of video signals which are reproduced from t~e rotary magnetic heads lA and lB
but not separated as yet into luminance signals and chrominance signals. The above example will be described with reference to Figure 5, in which elements corresponding to those of Figure 3 are similarly referred with the repeated description being omitted. In an apparatus of this embodiment, at the input sides of the buffer amplifiers 3A and 3B there are respectively connected reverse-L-shaped variable attenuators each consisting of a resistor 41A or 41B and a field effect transistor 40A or 40B serving as a variable impedance element thereby to form variable gain circuits 13A and 13B. The parallel circuit consisting of the series connection of capacitor 32A and field effect transistor 30A and the other series connection of capacitor 32B and field effect transistor 30B is connected at one end thereof respect-ively through resistors 34A and 34B to the gates of the field effect transistors 4~A and 40B while at its other end to the ground.
In this em~odiment, another ~ariable gain circuit ~06~54 13' ot~er than the afiove mentioned varia~le gain circuits 13A
and 13B is provided in the tran~m~tting path of chrominance signals, while ~he bur~t signal ~rom the burst gate circuit 35 is applied to an amplitude detector circuit 37' to perform the amplitude detection and a detected output therefrom is applied to the variable gain circuit 13' as a variable gain control signal. However, these circuits may also be omissible.
With the apparatus of Figure 5, there is an advantage such that the luminance signals Cor frequency-modulated luminance signals in this case~ from the respective rotary magnetic heads lA and lB are also made constant in level in addition to the fact that the chrominance signals from the same are made constant in level.
In the respective embodiments described above, the video signal reproducing apparatus has provided therein two rotary heads (N = 2~. However, the number N may be more than 3 and the number of the series connection consisting of capacitor and switching element is accordingly increased.
Besides, the switching element is not limited to a field effect 2Q transistor but various kinds of switching element such as a bipolar transistor or the like are also applicable thereto. The amplitude detector circuit is also not limited to the synchronous detector circuit.
According to the invention described above, the video signal reproducing apparatus having N (N is an integer equal or more than 2~ of rotary heads comprises a variable gain circuit provided in a transmitting path of reproduced video signals from said N num~er o~ rotary heads, an amplitude detector circuit to which a pilot signal separated from the reproduced video signals is applied, and N number of series circuits each consisting of series-connected capacitor and switching element and corresponding to N number of the rotary heads, in which an ;145~
output voltage of the amplitude detector circuit is impressed between both ends of a parallel circu~t consisting of N number of the series circuits to derive therefrom an output which is supplied to the variable gain circuit as a variable gain control signal, and the switc~ing elements of N num~er of series cir-cuits are respactivel~ controlled so as to be turned on only during a period where a reproduced video signal is obtained from a corresponding rotary head. Accordingly, in the video signal reproducing apparatus having N number of the rotary heads, lQ even though the reproduced video signals from N number of the rotary heads are varied in level, continuous reproduced video signals having constant level can ~e o~tained by removing the level fluctuation automatically. Further, the occurrence of color flicker is positively el~nated in the reproduced video signals or, if they are chrominance signals, in the reproduced pictures. As a result, it is possible to provide a reproduced color picture of good quality.
1^7hile the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of invention.
3~
The variable gain circuit 13 in this e}nbodiment is composed of a two-stage amplifier circuit having transistors 43 and 44 and a variable attenuator consisting of a resistor 41 and a variable impedance field effect transistor 40, both being connected in a reverse-L shape. The variable attenuator is provided at the input side of the first-stage transistor 43.
A series circuit consisting of a capacitor 32A and a field effect transistor 30A served as a switching element and another series circuit consisting of a capacitor 32B and a field effect transistor 30B served as a switching element are connected in parallel with each other, the parallel circuit being connected at one end thereof through a resistor 34 to the gate of the field effect transistor 40 of the circuit 13 and at the other end thereof to the ground.
These field effect transistors 30A and 30B are corresponding to the rotary magnetic heads lA and lB, respect-ively, each being controlled to be turned on only during the period ~here a reproduced video signal is being derived from the corresponding rotary magnetic head lA or lB. To this end, according to the rotation of the rotary magnetic heads lA and 3Q lB two pulse signals having phase different of 180 there-between are adapted to be obtaina~le at every rotation thereof and supplied to input terminals 25 and 26, respectively. These 10614S~
pulse signals are respectively applied to monostable multi-vi~rators 27 and 2 8 to be delayed for a predetermined time so as to correspond to the signal change-over times of the rotary magnetic heads lA and lB. Thereafter, these signals are applied to a flip-flop c~rcuit 29 to produce outputs having polarities different from each other, which are then applied to the bases of the field effect transistors 3QA and 30B, respectively, to turn-on the both alternately. In this case, one of these outputs from the flip-flop circuit 29is supplied to the switching circuit 4 as a switching control signal.
The ~urst signal from the burst gate circuit 35is also applied to a limiter circuit 36 serving as a wave shaping circuit to produce a rectangular-wave signal having constant amplitude which is applied as a control signal or a gate signal to a synchronous dete.ctor circuit 37 serving as an amplitude detector circuit.
The detector circuit 37 comprises a transistor 46 to which a signal from tne limiter circuit 36is applied for being amplified, a transformer 47 whose primary winding 47Ais 2Q connected to the collector of the transistor 46 and whose secondary winding 47Bis connected thereacross with a series connection consisting of a capacitor 49A, a diode 50A, a resis-tor 51A, a resistor 51B, a diode 50B and a capacitor 49B, and a series circuit consisting of resistors 52A and 52B which is connected between the connection mid-point of the diode 49A and the diode 50A and the connection mid-point of the diode 50B and the capacitor 49B. The connection mid-point of the resistors 51A and 51Bis applied with a E1ias from a variable resistor 55 and the burst signal from the burst gate circuit 35. Further, the mid-point of the secondary winding 47B of the transformer 47 is connected to the connection mid-point between the resistors 52A and 52B.
The output of the detector circu~t 37 is derived from the connection }nid-point of the resistors 52A and ~2B, that is, its output terminal and applied across both ends of the parallel circuit consisting of the series circuit of capacitor 32A and field effect transistor 30A and the series circuit of capacitor 32~3 and field effect transistor 30B. Reference character + B
represents a power source.
A description will next be given on the operation and effect of the apparatus shown in Figure 3. The field effect transistors 30A and 3QB each serving as a switching element are turned on respectively only during the period where the reproduced video signal is being derived from the corresponding rotary magnetic head lA or lB. On the other hand, the opposite ends of the secondary winding 47B of the transformer 47 are alternately inverted in polarity based on the outputs of the primary winding 4 7A . When the end portion of the secondary winding 47B at the side of capacitor 49B becomes positive in polarity, a signal flows through a loop of primary winding 47B-capacitor 49B - diode 50B - resistor 51B - resistor 51A - diode 2Q 50A - capacitor 49A - secondary winding 47B, so that the diodes 50A and 50B are turned on only during the period of half cycle of the signal at every half cycle thereof. Therefore, if the transformer 47 is previously adjusted, the half cycle period during which diodes 50A and 50s are being turned on can be conformed with, for example, a positive half cycle period of the burst signal. Accordingly, in this case, a portion of this burst signal at a positive half cycle flows through two paths of burst gate circuit 35 - resistors 51A, 51B - diodes 50A, 50B -capacitors 49A, 49B - middle point of secondary winding 47B to the capacitor 32A or 32B to charge the same up to the peak value of the burst signal. The voltage across the capacitor 32A or 32B is then applied through the resistor 34 to the gate of the _g _ 1061~54 field effect transistor 40 of t~e variable gain circuit 13. In this case, when the ~ield effect. transistors 3QA and 3QB are respectively in off-state, the voltages across the corresponding capacitors 32A and 32B are held at the values immediately before they are turned off. As a result, a variable control signal applied to the field effect transistor 40 becomes as shown in Figure 4 suc~ that slopes disappear at the pulse rising and falling portions between the output signals FA and FB corres-ponding to t~s respective rotary magnetic heads, that is, the pulse rising and falling times thereof become nearly zero.
Accordingly, the chrominance signal derived from the variable gain circuit 13 Cthat is, the chrominance signal converted into low frequency~ will have a constant level independent of the difference of the rotary magnetic heads lA and lB. In other words, even if video signals reproduced from the rotary magnetic heads lA and lB, that is, the chrominance signals in this case are of level variation type such as shown in Figure 1, the variable gain circuit 13 can yield chrominance signals such as having constant level and causing no jumping-up at a time point when the signals from the respective rotary magnetic heads lA
and lB are changed-over.
Furthermore, according to the present apparatus, the diodes 50A and 50B are turned on based on the signal having constant amplitude derived from the limiter circuit 36 and a portion of the ~urst signal at, for example, a positive half cycle is picked out according to these conductive diodes 50A
and 50B. merefore, a variable gain control signal of quick rising can be obtained without any time lag due to the threshold level of the diodes 50A and 50B being caused and also without any influence of d layed operation of the diodes 50A and 50B themselves being effected. As a re-sult, even if a reproduced chrominance signal is rapidly changed in level, the signal can be corrected to be constant in level with the result that there is no possibilitv of producing color shading on the reproduced picture.
lQ614S4 In addition, the phase con~ormab-lity ~etween the signal derived from t~ limiter circuit 36 and the ~urst signal can be ac~ieved only by adjusting the transformer 47 particu-larly with nocomplicated operation being required and with a simple construction, too.
The variable gain circuit 13 in Figure 3 may be provided at the output side of the band-pass filter 15. In this case, a chrominance signal having carrier frequency reconverted to the original value 3.58MHz will be made constant in level.
The apparatus in Figure 3 is described of the case ~here the variable gain circuit is provided in transmitting path of chrominance signals. However, it is also possible to provide variable gain circuits in transmitting paths of video signals which are reproduced from t~e rotary magnetic heads lA and lB
but not separated as yet into luminance signals and chrominance signals. The above example will be described with reference to Figure 5, in which elements corresponding to those of Figure 3 are similarly referred with the repeated description being omitted. In an apparatus of this embodiment, at the input sides of the buffer amplifiers 3A and 3B there are respectively connected reverse-L-shaped variable attenuators each consisting of a resistor 41A or 41B and a field effect transistor 40A or 40B serving as a variable impedance element thereby to form variable gain circuits 13A and 13B. The parallel circuit consisting of the series connection of capacitor 32A and field effect transistor 30A and the other series connection of capacitor 32B and field effect transistor 30B is connected at one end thereof respect-ively through resistors 34A and 34B to the gates of the field effect transistors 4~A and 40B while at its other end to the ground.
In this em~odiment, another ~ariable gain circuit ~06~54 13' ot~er than the afiove mentioned varia~le gain circuits 13A
and 13B is provided in the tran~m~tting path of chrominance signals, while ~he bur~t signal ~rom the burst gate circuit 35 is applied to an amplitude detector circuit 37' to perform the amplitude detection and a detected output therefrom is applied to the variable gain circuit 13' as a variable gain control signal. However, these circuits may also be omissible.
With the apparatus of Figure 5, there is an advantage such that the luminance signals Cor frequency-modulated luminance signals in this case~ from the respective rotary magnetic heads lA and lB are also made constant in level in addition to the fact that the chrominance signals from the same are made constant in level.
In the respective embodiments described above, the video signal reproducing apparatus has provided therein two rotary heads (N = 2~. However, the number N may be more than 3 and the number of the series connection consisting of capacitor and switching element is accordingly increased.
Besides, the switching element is not limited to a field effect 2Q transistor but various kinds of switching element such as a bipolar transistor or the like are also applicable thereto. The amplitude detector circuit is also not limited to the synchronous detector circuit.
According to the invention described above, the video signal reproducing apparatus having N (N is an integer equal or more than 2~ of rotary heads comprises a variable gain circuit provided in a transmitting path of reproduced video signals from said N num~er o~ rotary heads, an amplitude detector circuit to which a pilot signal separated from the reproduced video signals is applied, and N number of series circuits each consisting of series-connected capacitor and switching element and corresponding to N number of the rotary heads, in which an ;145~
output voltage of the amplitude detector circuit is impressed between both ends of a parallel circu~t consisting of N number of the series circuits to derive therefrom an output which is supplied to the variable gain circuit as a variable gain control signal, and the switc~ing elements of N num~er of series cir-cuits are respactivel~ controlled so as to be turned on only during a period where a reproduced video signal is obtained from a corresponding rotary head. Accordingly, in the video signal reproducing apparatus having N number of the rotary heads, lQ even though the reproduced video signals from N number of the rotary heads are varied in level, continuous reproduced video signals having constant level can ~e o~tained by removing the level fluctuation automatically. Further, the occurrence of color flicker is positively el~nated in the reproduced video signals or, if they are chrominance signals, in the reproduced pictures. As a result, it is possible to provide a reproduced color picture of good quality.
1^7hile the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of invention.
3~
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED, ARE DEFINED AS FOLLOWS:
1. A gain control circuit for a video signal reproducing apparatus comprising a plurality of trans-ducers to reproduce recorded video signals, said circuit comprising:
A. a plurality of variable gain circuits each connected to a respective one of said transducers to receive reproduced video signals therefrom;
B. means to separate a predetermined signal from the reproduced video signals;
C. an amplitude detector circuit connected to the signal separating means; and D. a plurality of series circuits corresponding in number to the number of said transducers and each comprising a capacitor and a switching element connected in series, all of the series circuits being connected in parallel to a common junction to form a parallel circuit, said common junction being connected to the output of the amplitude detector circuit to have the output voltage of the detector circuit impressed across the parallel circuit, said common junction being further connected to all of the variable gain circuits to simultaneously supply said detector circuit output to all of said variable gain circuits to control the gains thereof, and means for selectively energizing each switching element in each of the series circuits to cause each of the series circuits to be conductive only when a reproduced video signal from the respective transducer corresponding to the series circuit is applied to the respective variable gain circuit so that the voltage at said common junction is substantially the same during transition intervals between respective transducer outputs.
A. a plurality of variable gain circuits each connected to a respective one of said transducers to receive reproduced video signals therefrom;
B. means to separate a predetermined signal from the reproduced video signals;
C. an amplitude detector circuit connected to the signal separating means; and D. a plurality of series circuits corresponding in number to the number of said transducers and each comprising a capacitor and a switching element connected in series, all of the series circuits being connected in parallel to a common junction to form a parallel circuit, said common junction being connected to the output of the amplitude detector circuit to have the output voltage of the detector circuit impressed across the parallel circuit, said common junction being further connected to all of the variable gain circuits to simultaneously supply said detector circuit output to all of said variable gain circuits to control the gains thereof, and means for selectively energizing each switching element in each of the series circuits to cause each of the series circuits to be conductive only when a reproduced video signal from the respective transducer corresponding to the series circuit is applied to the respective variable gain circuit so that the voltage at said common junction is substantially the same during transition intervals between respective transducer outputs.
2. The gain control circuit of Claim 1 in which each of the switching elements is a field-effect transistor.
3. The gain control circuit of Claim 1 comprising filter means connected to receive output signals from the gain control circuits and to separate the video signals from the gain control circuits into a luminance signal and a chrominance signal.
4. The gain control circuit of Claim 1 comprising a filter circuit connected between the transducers and the respective variable gain circuits and having band-pass characteristics to apply only chrominance signals of the video signals to the respective variable gain circuits.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6457873A JPS5549479B2 (en) | 1973-06-08 | 1973-06-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1061454A true CA1061454A (en) | 1979-08-28 |
Family
ID=13262243
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA201,905A Expired CA1061454A (en) | 1973-06-08 | 1974-06-07 | Gain control device of video signal reproducing apparatus |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US3949414A (en) |
| JP (1) | JPS5549479B2 (en) |
| CA (1) | CA1061454A (en) |
| DE (1) | DE2427591A1 (en) |
| FR (1) | FR2232873B1 (en) |
| GB (1) | GB1468894A (en) |
| IT (1) | IT1014882B (en) |
| NL (1) | NL7407663A (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5110543B1 (en) * | 1970-11-25 | 1976-04-05 | ||
| JPS587117B2 (en) * | 1975-10-01 | 1983-02-08 | ソニー株式会社 | Irosingou Shiyori Cairo |
| JPS5514726A (en) * | 1978-07-19 | 1980-02-01 | Hitachi Ltd | Magnetic recorder/reproducer |
| US4396953A (en) * | 1979-12-06 | 1983-08-02 | Victor Company Of Japan, Ltd. | Color video signal dubbing system for collating the outputs of signal sources |
| JPS5765988A (en) * | 1980-10-13 | 1982-04-21 | Victor Co Of Japan Ltd | Processing circuit for color video signal |
| US4500931A (en) * | 1981-02-25 | 1985-02-19 | Tokyo Shibaura Denki Kabushiki Kaisha | Signal sampling gate circuit |
| US4433255A (en) * | 1981-02-25 | 1984-02-21 | Tokyo Shibaura Denki Kabushiki Kaisha | Signal sampling gate circuit |
| JPS5990477A (en) * | 1982-11-16 | 1984-05-24 | Sony Corp | Video signal correcting circuit |
| JPS6223293A (en) * | 1985-07-23 | 1987-01-31 | Victor Co Of Japan Ltd | Video signal reproducing device |
| JPS6482306A (en) * | 1987-09-24 | 1989-03-28 | Toshiba Corp | Data reproducing device |
| JPH0467415A (en) * | 1990-07-06 | 1992-03-03 | Sony Corp | Recording/reproducing device |
| GB2257868B (en) * | 1991-07-16 | 1995-04-12 | Asahi Optical Co Ltd | Still video device |
| DE4201564A1 (en) * | 1992-01-22 | 1993-07-29 | Thomson Brandt Gmbh | CIRCUIT FOR CONTROLLING THE COLOR CARRIER AMPLITUDE IN A VIDEO RECORDER |
| CN1051899C (en) * | 1992-10-28 | 2000-04-26 | 三星电子株式会社 | Chroma burst detection system |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1468045A (en) * | 1965-03-12 | 1967-02-03 | Ampex | Standardization device for magnetic recording device |
| US3381083A (en) * | 1965-03-12 | 1968-04-30 | Ampex | Magnetic recorder equalization system having continually adjusted compensation |
| AT257707B (en) * | 1966-01-19 | 1967-10-25 | Philips Nv | Device for recording and reproducing video information |
| US3541237A (en) * | 1966-10-19 | 1970-11-17 | Fernseh Gmbh | Control arrangement for color television |
| US3702374A (en) * | 1969-04-17 | 1972-11-07 | Sony Corp | Color video signal recording and reproducing apparatus with pilot signal for automatic color control |
| US3585280A (en) * | 1969-06-11 | 1971-06-15 | Columbia Broadcasting Syst Inc | Gain correction apparatus for color picture information signals reproduced from a record medium |
| JPS4932445B1 (en) * | 1970-03-25 | 1974-08-30 | ||
| US3643013A (en) * | 1970-10-08 | 1972-02-15 | Ampex | Dual loop equalization for a frequency modulated signal system |
| US3717721A (en) * | 1970-10-14 | 1973-02-20 | Nippon Electric Co | Automatic chroma compensating system |
| US3852808A (en) * | 1973-04-04 | 1974-12-03 | Rca Corp | Color amplitude correction in plural transducer signal playback systems |
| JPS5325721B2 (en) * | 1973-11-07 | 1978-07-28 |
-
1973
- 1973-06-08 JP JP6457873A patent/JPS5549479B2/ja not_active Expired
-
1974
- 1974-06-04 US US05/476,277 patent/US3949414A/en not_active Expired - Lifetime
- 1974-06-05 GB GB2497974A patent/GB1468894A/en not_active Expired
- 1974-06-07 IT IT23755/74A patent/IT1014882B/en active
- 1974-06-07 NL NL7407663A patent/NL7407663A/xx not_active Application Discontinuation
- 1974-06-07 CA CA201,905A patent/CA1061454A/en not_active Expired
- 1974-06-07 DE DE19742427591 patent/DE2427591A1/en not_active Ceased
- 1974-06-10 FR FR7420018A patent/FR2232873B1/fr not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| FR2232873B1 (en) | 1978-06-02 |
| GB1468894A (en) | 1977-03-30 |
| FR2232873A1 (en) | 1975-01-03 |
| DE2427591A1 (en) | 1975-01-02 |
| JPS5015426A (en) | 1975-02-18 |
| NL7407663A (en) | 1974-12-10 |
| JPS5549479B2 (en) | 1980-12-12 |
| IT1014882B (en) | 1977-04-30 |
| US3949414A (en) | 1976-04-06 |
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